Fiber redirect system, multi-axis robotic wrist and fiber placement apparatus incorporating same and related methods

ABSTRACT

A fiber redirect system for use with a multi-axis robotic wrist and fiber placement system and methods of using the same are provided. The fiber redirect system may include one or more redirect mechanisms configured to alter the path of one or more fiber tows fed from a creel assembly to a fiber placement head. The redirect mechanism may be located and configured so as to be centered about either the intersection of the pitch and yaw axes of the robotic wrist or the intersection of the yaw and roll axes of the robotic wrist. In one exemplary embodiment, a first redirect mechanism is centered about the intersection of the pitch and yaw axes, a second redirect mechanism is centered about the intersection of the yaw and roll axes and a third redirect mechanism may be centered about the roll axis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods of fiber placementand fiber placement machines and, more specifically, to fiber redirectsystems and associated multi-axis robotic wrists utilized with suchfiber placement methods and machines.

2. State of the Art

Fiber placement is generally a technique of placing a band of fibers,such as a plurality of preimpregnated fiber tows, onto the surface of amandrel or on an overlying work piece to form a composite structure.Fiber placement offers various advantages in forming a compositestructure including the ability of placing a band of fibers at variousangles, widths and lengths onto variously shaped contours and surfaces.Thus, fiber placement enables the fabrication of composite structureswhich exhibit complex shapes and surfaces while simultaneously enablingthe band of fibers to be located and oriented in a structurally desiredorientation and configuration.

Fiber placement systems generally include a supply of fiber tows,referred to herein as a creel or creel assembly. Individual tows offiber are supplied from the creel assembly and fed to a robotic wristwhich includes a placement or delivery head. The robotic wristconventionally allows positioning of the placement head by articulatingthe wrist about multiple axes. For example, a multi-axis robotic wristmay allow movement about three orthogonal axes conventionally referredto as yaw, pitch and roll axes.

In feeding the fiber tows from a creel assembly to the placement, it isdesirable to maintain at least a minimum level of tension within thefiber tows such that they remain relatively taut. Without such tension,the fiber tows may become twisted, displaced and/or damaged. At best,such results cause a delay in the fiber placement process and requireadditional maintenance of the fiber placement system by an operatorthereof. However, a damaged or otherwise improperly placed fiber tow orsegment thereof may ultimately result in a defective compositestructure.

The fiber path of the individual tows between the creel assembly and theplacement head usually includes the passing of the fiber tows around oneor more redirect rollers. The redirect rollers enable the fiber tows tochange directions and, also, to accommodate the changing positions andorientations of the robotic wrist as it positions the placement head forapplication of the fiber tows to a desired surface. In some prior artsystems, redirect rollers are coupled to servo motors or otherpositioning devices to enable independent positioning of the redirectrollers in an attempt to define and redefine the path of the fiber towsdepending on, for example, the position and orientation of the roboticwrist and its associated placement head.

However, the use of such redirect rollers has not been entirelysuccessful in maintaining the fiber tows in a relatively taut condition.For example, as a robotic wrist positions itself at the limits of travelabout its yaw, pitch and roll axes, the path of the fiber tows isconventionally lengthened, causing an additional length of material tobe fed from the creel assembly for the individual tows. However, as therobotic wrist becomes relatively more retracted in its yaw, pitch androll positions, the fiber path is conventionally shortened orcontracted, causing the individual fiber tows to exhibit an amount ofslack between the creel assembly and the placement head. Such slack mayultimately result in a fiber tow becoming unacceptably twisted, damagedor displaced from its individual path about the various redirectrollers.

While mechanisms, such as the above-mentioned servo motor positioningsystem, have been utilized in an attempt to better control the changingpath of the fiber tows, such systems have been limited in their successand, further, introduce additional complexities and costs into fiberplacement systems. For example, such mechanisms may require complicatedcomputer control to correlate the movements of such a mechanism with themovements of the robotic wrist and placement head. Additionally, suchmechanisms introduce additional issues of maintenance for the operatorof the fiber placement equipment.

A somewhat related issue with regard to multi-axis robotic wristsincludes the harnessing of numerous electrical cables or othertransmission lines (e.g., hydraulic or pneumatic tubing) coupled withthe various controls, sensors, motors and other actuators associatedwith the wrist and placement head. Again, as a multi-axis robotic wristarticulates through its various ranges of motion, such transmissionlines exhibit a certain amount of slack so as to avoid overextension andtensile failure thereof. Thus, with the transmission lines exhibitingslack from time to time, depending on the position of the robotic wrist,such transmission lines may undesirably catch on a protruding object orotherwise become tangled in some manner.

In view of the shortcomings in the art, it would be advantageous toprovide a fiber placement system, including a fiber redirect system androbotic wrist, which minimizes the change in length of the fiber pathbetween, for example, a creel assembly and a placement head whileaccommodating the various positions, orientations and configurations therobotic wrist and placement head may assume.

Additionally, it would be advantageous to provide a fiber placementsystem having a fiber redirect system which does not require additionalpositioning mechanisms such as, for example, servo motors, withattendant computer control of the same. Rather, it would be advantageousto have such a redirect system continuously control the fiber pathautomatically, based on the position and orientation of the roboticwrist and placement head, without independent control of the redirectmechanisms.

BRIEF SUMMARY OF THE INVENTION

In accordance with one aspect of the invention a fiber redirect systemis provided for use in association with a multi-axis robotic wrist and afiber placement system. The fiber redirect system includes at least oneredirect mechanism configured to alter a path of at least one fiber towengaged therewith. The at least one redirect mechanism is centered abouteither an intersection of a pitch axis and a yaw axis of the multi-axisrobotic wrist or an intersection of a roll axis and the yaw axis of themulti-axis robotic wrist.

In one exemplary embodiment, the at least one redirect mechanism mayinclude a first redirect mechanism which is centered about theintersection of the pitch and yaw axes, a second redirect mechanismcentered about the intersection of the yaw and roll axes and a thirdredirect mechanism centered about the roll axis.

In accordance with another aspect of the present invention, a roboticwrist for a fiber placement system is provided. The robotic wristincludes a first section, a second section coupled with the firstsection and a third section coupled with the second section. The first,second and third sections are configured to articulate about a pitchaxis of the robotic wrist. The second and third sections are configuredto articulate about a yaw axis of the robotic wrist. The third sectionis configured to articulate about a roll axis of the robotic wrist. Atleast one redirect mechanism is centered about either an intersection ofthe pitch axis and the yaw axis or an intersection of the yaw axis andthe roll axis and is configured to alter the path of at least one fibertow engaged therewith.

In accordance with yet another aspect of the present invention, a fiberplacement system is provided. The fiber placement system includes acreel assembly including a supply of at least one fiber tow. A fiberplacement system also includes a robotic wrist such as described aboveincluding at least one redirect mechanism centered about either theintersection of a pitch axis and a yaw axis or the intersection of theyaw axis and a roll axis. Additionally, the fiber placement system mayinclude a structural platform on which the robotic wrist is movablypositioned.

In accordance with a further aspect of the present invention, a methodis provided for conveying at least one fiber tow from a creel assemblyto a placement head of a fiber placement system. The method includescoupling a robotic wrist with the placement head and configuring therobotic wrist to be movable about a pitch axis, a yaw axis and rollaxis. A first redirect mechanism is configured to be centered about anintersection of the pitch axis and yaw axis and a second redirectmechanism is configured to be centered about an intersection of the yawaxis and the roll axis. The at least one fiber tow is passed from thecreel assembly to the first redirect mechanism, from the first redirectmechanism to the second redirect mechanism and from the second redirectmechanism to the placement head.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing and other advantages of the invention will become apparentupon reading the following detailed description and upon reference tothe drawings in which:

FIG. 1 is a perspective of a fiber placement system in accordance withan embodiment of the present invention;

FIG. 2A is a rear perspective of a robotic wrist according to anembodiment of the present invention;

FIG. 2B is a side elevational view of the robotic wrist shown in FIG.2A;

FIG. 2C is front partial cross-sectional view of the robotic wrist shownin FIG. 2A;

FIG. 2D is a plan view of the robotic wrist shown in FIG. 2A;

FIGS. 3A and 3B show a roller assembly which may be used with a roboticwrist in accordance with an embodiment of the present invention;

FIG. 4A is a side elevational schematic of a fiber redirect systemincluding an associated fiber path in accordance with an embodiment ofthe present invention;

FIG. 4B is a rear elevational schematic of the fiber redirect system andassociated fiber path shown in FIG. 4A; and

FIG. 4C is a geometric diagram showing the relationship of various fibertows in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a fiber placement system 100 is shown in accordancewith an embodiment of the present invention. The fiber placement system100 includes a creel assembly 102 having, for example, multiple sources104 of individual fiber tows 106 such as, for example, tows ofpreimpregnated carbon fiber or other prepreg materials. A tensioningsystem may also be associated with the creel assembly 102 including aplurality of individual tensioners 108, each associated with anindividual fiber tow 106. An exemplary tensioning system is disclosed inU.S. Pat. No. 6,491,773 B1 assigned to the assignee of the presentinvention and entitled POSITION CONTROLLED TENSIONER SYSTEM, issued Dec.10, 2002, the disclosure of which is incorporated herein by reference inits entirety.

The individual fiber tows 106 are gathered to a central location 110 andgenerally collimated into one or more bands of substantially paralleland laterally spaced tows 106, referred to herein as tow bands 112. Itis noted that FIG. 1 shows a single tow band 112 being formed of theindividual fiber tows 106. Additionally, it is noted that FIG. 1 showseight individual tows 106 being fed from the creel assembly 102.However, such are merely exemplary for purposes of illustration and, aswill be discussed in greater detail below, the use of multiple tow bands112, as well as tow bands 112 formed of other numbers of individual tows106, are clearly within the scope of the present invention.

The tow band 112 extends from the central location 110 to a roboticwrist 114, through the robotic wrist 114 through a delivery system 115to a fiber placement head 116. The delivery system may includemechanisms for cut/clamp and restart of individual fiber tows 106. Asknown to those of ordinary skill in the art, the use of cut/clamp andrestart mechanisms enable individual payout control of the fiber tows106 providing for varied width tow bands 112 to be fed through theplacement head 116.

The robotic wrist 114 is located on a structural platform 118 which mayalso be referred to as a gantry. The robotic wrist 114 may be variablypositionable relative to the structural platform 118, such as along aset of tracks 120. The structural platform 118, or portions thereof, mayalso be variably positionable along one or more axes so as to affordconsiderable flexibility in positioning the robotic wrist 114 and itsassociated placement head 116, as will be appreciated by those of skillin the art. Additionally, as will be discussed in greater detail below,the robotic wrist 114 is configured for positioning, relative to thestructural platform, about multiple axes.

It is noted that, while the fiber placement system 100, shown anddescribed with respect to FIG. 1, includes a gantry or structuralplatform 118, other configurations, such as the use of a boom coupledwith the robotic wrist 114, may also be adapted for use with the presentinvention as will be appreciated by those of skill in the art.

The tow band 112 (or bands, as the case may be) may be somewhatconsolidated, or more tightly collimated, as they are fed into theplacement head such that each fiber tow 106 is substantially laterallycontiguous with each adjacent fiber tow 106. The placement head 116 maythen selectively apply a segment of the consolidated tow band 112 to alocation over the surface of a mandrel 122, or over a surface of a workpiece 124 being formed on the mandrel 122 such placement being eitherdirectly on the mandrel 122 or work piece 124 or over a previouslyapplied fiber layer or other component. The mandrel 122 and associatedwork piece 124 may be held and positioned by a head stock 126A and atail stock 126B. The head stock 126A and tail stock 126B may beconfigured and located to rotate the mandrel 122 and work piece 124about a specified axis 128, and may further be configured to displacethe mandrel 122 and work piece 124 along additional axes of movement, ifso desired.

In applying the fiber tows 106 to the mandrel 122 or work piece 124,such as in the form of a consolidated fiber tow band, the placement head116 may heat the tow band 112 to effect a partial cross-linking of theindividual tows 106 with each other as well as with the surface of thework piece 124. Additionally, a consolidating member 127, such as aroller, a shoe or a shaped platen may be used to press the tow band 112onto the surface of the mandrel 122 or work piece 124 or previouslyapplied fibers or other components to remove voids therebetween. Theplacement head 116 may apply the fiber tows 106 such that they exhibit adesired fiber orientation, width and/or length. Thus, work pieces 124,exhibiting complex shapes and surface geometries, may be constructed byplacing and orienting the fibers in a desired configuration for purposesof strength and structural integrity.

In placing the fiber tows 106 to the mandrel 122 or work piece 124, itmay generally be desirable to orient the placement head 116substantially normal to the surface to which the fiber tows 106 arebeing placed. Thus, in order to effectively position the placement head116 for application of the fiber tows 106 on the surface of the mandrel122 or work piece 124, the robotic wrist 114 is configured to articulateabout multiple axes. For example, the robotic wrist 114 may beconfigured to rotate about a first axis 130, referred to herein as thepitch axis. Further, the wrist 114 may be configured to rotate about asecond axis 132, referred to herein as the yaw axis. Additionally, therobotic wrist 114 and, more specifically an upper section of the roboticwrist 114 including the delivery system 115 and placement head 116, maybe configured to rotate about a third axis 134, referred to herein asthe roll axis.

The various axes of rotation may be oriented in a specified geometricrelationship relative to one another. For example, the pitch axis 130may intersect the yaw axis 132 at a substantially perpendicular angle.Similarly, the roll axis 134 may intersect the yaw axis 132 at asubstantially perpendicular angle. Further, the roll axis 134 may bedisplaced a defined distance along the yaw axis 132 from theintersection of the yaw and roll axes 132 and 134 while also beingoriented at a substantially perpendicular angle relative to the pitchaxis 130.

The robotic wrist 114 may be rotated about the various axes 130, 132 and134 by actuators 136, 138 and 140 which may include, for example,electric motors and associated gearing, although other mechanisms may beused as will be appreciated by those of skill in the art. In oneexemplary embodiment, the robotic wrist 114 may be able to rotateapproximately 60° up (or back) and 50° down (or forward) about the pitchaxis 130, approximately ±95° about the yaw axis 132 and approximately±150° about the roll axis 134 relative to a substantially neutralposition such as that shown in FIG. 1.

The fiber placement system 100 may be operatively coupled with a controlsystem 150, shown schematically in FIG. 1, which may be used to controlthe various systems and components such as, for example, the creelassembly 102 and its associated tensioning system, the robotic wrist 114and its various components, the head stock 126A and/or tail stock 126Band even the positioning of the structural platform 118 relative to themandrel 122 and work piece 124. Such control may be effected by, forexample, a computer through computer numeric control (CNC) techniques orother similar control systems, as will be appreciated by those ofordinary skill in the art.

Referring now to FIGS. 2A–2D, various views of the robotic wrist 114 ofthe present invention are shown without the delivery system 115 orplacement head 116 (FIG. 1) for purposes of convenience and clarity inillustration. It is noted that FIG. 2A is a rear perspective of therobotic wrist 114, FIG. 2B is a side elevation of the robotic wrist 114,FIG. 2C is a front elevational view in partial cross section of therobotic wrist 114 and FIG. 2D is a plan view of the robotic wrist 114.

As previously noted, the robotic wrist 114 is configured to rotate aboutvarious axes 130, 132 and 134. More specifically, the robotic wrist maybe described as having three general sections including a lower section160, a mid-section 162 and an upper section 164 wherein at least one ofthe three general sections 160, 162 and 164 rotate about each of thedefined axes of rotation 130, 132 and 134. Thus, for example, all threesections 160, 162 and 164 may be configured for rotation about the pitchaxis 130; the mid-section 162 and upper section 164 may be configured torotate about the yaw axis 132; and the upper section 164 may beconfigured to rotate about the roll axis 134.

It is further noted that the axes 130, 132 and 134 may move relative toother components of the fiber placement system 100 (FIG. 1) whilemaintaining their geometric configuration relative to one another. Thus,for example, when the lower, mid- and upper sections are rotated aboutthe pitch axis 130, the yaw and roll axes 132 and 134 are also rotatedabout the pitch axis 130 and thus relative to, for example, thestructural platform 118 (see FIG. 1) but maintain their geometricrelationship with the pitch axis 130.

FIGS. 2A–2D show an embodiment wherein multiple tow bands, shown as anupper tow band 112A and a lower tow band 12B, are fed through therobotic wrist 114 to the delivery system 115 and placement head 116(FIG. 1). The tow bands 112A and 112B, which each include a plurality oftows 106 as discussed above herein, travel from a location behind therobotic wrist 114 to a first redirect mechanism 170, referred to hereinas the pitch redirect mechanism, and which may include a pair ofredirect rollers 172A and 172B. The pitch redirect mechanism 170 enablesthe tow bands 112A and 112B to change direction of travel as they passthrough the robotic wrist 114. Furthermore, while FIGS. 2A–2D show thetow bands 112A and 112B changing direction from a substantiallyhorizontally oriented path prior to engagement with the pitch redirectmechanism 170 to a substantially vertically oriented path subsequent toengagement with the pitch redirect mechanism 170, the pitch redirectmechanism enables the path of the tow bands 112A and 112B to adapt toany of the robotic wrist's changing positions. As will be discussed ingreater detail below, the pitch redirect mechanism 170 is centered aboutthe intersection of the pitch and yaw axes 130 and 132.

The tow bands 112A and 112B extend from the pitch redirect mechanism 170through an opening 174 defined by a yaw bearing 176 to a second redirectmechanism 178, referred to herein as the yaw redirect mechanism. The yawredirect mechanism 178 may also include a pair of redirect rollers 180Aand 180B configured to redirect the path of the tow bands 112A and 1121Brespectively. Furthermore, while FIGS. 2A–2D show the tow bands 112A and112B changing from a substantially vertically oriented path prior toengagement with the yaw redirect mechanism 178 to a substantiallyhorizontally oriented path subsequent to engagement with the yawredirect mechanism rollers 172A and 172B, the yaw redirect mechanism 178allows the path of the tow bands 112A and 112B to adapt to any of therobotic wrists changing positions. As will be discussed in greaterdetail below, the yaw redirect mechanism 178 is centered about theintersection of the yaw and roll axes 132 and 134.

The tow bands 112A and 112B travel from the yaw redirect system throughan opening 182 defined in roll bearing 184 to another redirect mechanism186 (FIGS. 2B and 2D) referred to herein as the roll redirect mechanism.The roll redirect mechanism 186 mechanism may include a pair of redirectrollers 188A and 188B configured such that the individual fiber tows 106of each band 112A and 112B are spaced apart from adjacent tows 106 adistance equal to the nominal width of the fiber tows 106. Thus, as thetow bands 112A and 112B extend beyond the roll redirect mechanism 186,the tows 106 of the upper tow band 112A may be redirected to convergewith and commingle with the redirected tows 106 of the lower tow band112B to form a single collimated tow band 190 comprising all of the tows106 fed from the creel assembly 102 (FIG. 1). As will be discussed infurther detail below, the roll redirect mechanism 186 is centered aboutthe roll axis 134.

It is noted that none of the redirect mechanisms 170, 178 and 186require additional actuators or control mechanisms to position themindependent of and relative to the robotic wrist 114. Rather, eachredirect mechanism 170, 178 and 186 is configured to include simplemechanical members which stay in a fixed position relative to theportion of the robotic wrist to which each is attached (e.g., the lowersection 160, mid-section 162 or upper section 164).

Referring to FIGS. 3A and 3B, an exemplary roller assembly 200 is shownwhich may be used, for example, as a roller 172A, 172B, 180A, 180B,188A, 188B or other equivalent roller, in conjunction with one or moreof the above described redirect mechanisms 170, 178 and 186 and whichshows the simplicity of the redirect mechanisms of the presentinvention. The roller assembly 200 may include a plurality of individualrollers or pulleys 202 coupled to a shaft 204 by way of bearings 206such that each pulley 202 may rotate independently of the other pulleys202. Each pulley 202 includes a groove 208 formed about the outerperiphery thereof for receiving a fiber tow therein. It is noted thatthe roller assembly 200 shown includes sixteen individual pulleys 202.Again, such is simply exemplary and other configurations arecontemplated. For example, a roller assembly 200 utilized in connectionwith the redirect mechanisms 170, 178 and 186 shown and described withrespect to FIGS. 2A–2D need only include eight individual pulleys 202commensurate with the number of tows being directed therethrough.

The roller assembly 200 may further include adjustable mounting plates210 coupled to the shaft 204. The mounting plates 210 may be coupled toa section of the robotic wrist 114 (FIGS. 2A–2D) such as by fasteners212. The roller assembly 200 may thus be adjusted by loosening thefasteners and rotating the roller assembly 200 through a defined rangeof motion provided by the slots 213 formed in the mounting plates 210.Thus, the roller assembly 200 and, more particularly, the plurality ofpulleys 202 may be adjusted, relative to a given axis of rotation of thewrist (e.g., the pitch axis 130) and then fixed into the selectedposition by the fasteners 212. A guide member 214 may be positionedacross the face of the roller assembly 200 so as to maintain the fibertows 106 (FIGS. 2A–2D) within the grooves 208 of the pulleys should thefiber tows exhibit slack at any given time while the robotic wrist 114(FIGS. 2A–2D) articulates through its range of motions.

It is noted that by configuring the pulleys 202 to exhibit a relativelysmall diameter, the roller assemblies 200 may have their shafts 204, andthus their own rotational axes, positioned closer to the intersection ofthe centerline of the robotic wrist's axes of rotation (e.g., theintersection of the pitch and yaw axes 130 and 132). By placing theroller assemblies 200 closer to the intersection of the robotic wrist'saxes of rotation, the path of the fiber tows 106 may more closely trackthe actual axes of rotation 130, 132 and 134. However, depending on thetype of fiber tows 106 (FIGS. 2A–2D) being utilized, it may be desirableto maintain a minimum pulley diameter so as to not induce unwantedstress in the fiber tows 106 as they travel and bend thereabout. Thus,in one embodiment, an exemplary pulley 202 may exhibit a diameter ofapproximately 3.5 inches with a groove 208 formed in its outer peripheryof approximately 0.25 inch deep resulting in an effective turningsurface diameter for engagement by a fiber tow 106 of approximately 3.0inches.

Referring back to FIGS. 2A–2D, it is noted that, as the mid- and uppersections 162 and 164 rotate about the yaw axis 132, the sections of thetow bands 112A and 112B extending between the pitch redirect mechanism170 and the yaw redirect mechanism 178 will twist about the yaw axis132. This is because the pitch redirect mechanism 170 is fixed to thelower section 160 of the robotic wrist 114 and does not rotate about theyaw axis 132 while the yaw redirect 178 does rotate about the yaw axis132 with the mid-section 162. Similarly, as the upper section 164rotates about the roll axis 134, the sections of the tow bands 112A and112B extending between the yaw redirect mechanism 178 and the rollredirect mechanism 186 will twist about the roll axis 134. Thesetwisting motions cause differential pay out of the individual fiber tows106. However, due to the configuration of the redirect mechanisms 170,178 and 186 and, more particularly, due to the centering of the redirectmechanisms about the rotational axes 130, 132 and 134, the differentialpay out of the individual fiber tows 106 is minimized such that minimalslack occurs within the fiber tows 106 as they extend between the creelassembly 102 and the placement head 116 (FIG. 1).

For example, FIG. 4A shows a side elevational view of the tow bands 112Aand 112B as they travel through their respective paths. As noted above,the pitch redirect mechanism 170 is centered about the intersection ofthe pitch and yaw axes 130 and 132. This does not mean that the axes ofrotation of the redirect rollers 172A and 172B are equal distances fromthe intersection of the pitch and yaw axes 130 and 132. To the contrary,the redirect rollers 172A and 172B are strategically positioned so thefiber paths of the tow bands 112A and 112B are equally positioned aboutthe intersection of the pitch and yaw axes 130 and 132.

Similarly, the yaw redirect mechanism 178 is centered about theintersection of the yaw and roll axes 132 and 134 such that the fiberpaths of the tow bands 112A and 112B are substantially equal distancesfrom the intersection of the yaw and roll axes 132 and 134. Furthermore,the roll redirect mechanism 186 is centered about the roll axis 134 suchthat the fiber paths of the tow bands 112A and 112B are centered aboutthe roll axis.

Referring briefly to FIG. 4B, the redirect mechanisms 170 and 178 arealso configured such that the width of the tow bands 112A and 112B (onlyone tow band 112A is shown in FIG. 4B for clarity) are centered aboutthe axes of rotation 130, 132 and 134. Thus, for example, with a towband 112A including eight individual fiber tows 106, the fiber tows 106are symmetrically arranged relative to the yaw axis 132. Thus, forexample, the two outermost fiber tows 106, are substantially equaldistances from the yaw axis 132. Similarly, the two innermost fiber tows106 are substantially equal distances from the yaw axis 132. Similarrelationships are maintained with respect to the pitch and roll axes 130and 132. Such a configuration defines what may be termed a collectivefiber path for the multiple tow bands 112A and 112B wherein theplurality of tows 106 (whether configured as a single tow band or asmultiple tow bands) remain substantially symmetrical about thecollective fiber path. Furthermore, the collective fiber path of thepresent invention substantially follows the centerlines or axes ofrotation 130, 132 and 134 of the robotic wrist 114 (FIGS. 2A–2D)regardless of the orientation of the robotic wrist 114.

Referring back to FIG. 4A, as the robotic wrist 114 (FIGS. 2A–2D)rotates about the pitch axis 132, the segments of tow bands 112A and112B extending between the pitch redirect mechanism 170 and yaw redirectmechanism 178 maintain substantially constant lengths, which lengths aregenerally defined by the distance along the yaw axis 132 extendingbetween the pitch axis 130 and the roll axis 134.

Furthermore, referring back to FIG. 4B, as the robotic wrist 114 (FIGS.2A–2D) rotates about the yaw axis 132, the pay out of an individualfiber tow 106 is determined largely by the lateral distance between aspecific fiber tow 106 and the yaw axis 132. For example, a first fibertow 106A is a first distance D₁ from the yaw axis 132 while a secondfiber tow 106B is a second larger distance D₂ from the yaw axis 132. Asshown in FIG. 4C, this relationship defines a first turning angle θ₁ forthe first fiber tow 106A and a second turning angle θ₂ for the secondfiber tow 106B. Thus, as will be appreciated by those of ordinary skillin the art, the amount of pay out experienced by a given fiber tow 106due to rotation about the yaw axis 132 will be determined by the cosineof the turning angle of the fiber tow 106 (e.g., cos θ₁ or cos θ₂ ).Thus, by minimizing the distance of the fiber tows 106 from the yaw axis132 or, in other words, by minimizing the allowed turning angle θ, thepay out of the fiber tows 106 will also be minimized. In one embodiment,for example, the maximum allowed fiber tow turning angle θ may beapproximately 9°. Of course such an arrangement is exemplary and otherconfigurations are contemplated as being within the scope of theinvention.

Similar relationships may be maintained between the yaw redirectmechanism 178 and the roll redirect mechanism 186 to minimize the payout of individual fiber tows 106 associated with the turning angles ofthe fiber tows 106 extending therebetween.

It is noted that while the embodiments shown and described with respectto FIGS. 2A–2D and 3A–3C have employed two different tow bands 112A and112B, the present invention may be applied to configurations utilizingthree or more tow bands or even with a single tow band. Such embodimentswould still include pitch and yaw redirect mechanisms 170 and 178centered about the various intersections of axes of rotation (i.e., theintersection of the pitch and yaw axes 130 and 132 and the intersectionof the yaw and roll axes 132 and 134 respectively) with the rollredirect mechanism 186 being centered about the roll axis 134 to effecta collective fiber path which passes through and is centered about thevarious axes 130, 132 and 134.

Referring back to FIG. 1 and FIG. 2A another feature of the presentinvention is shown. In controlling the robotic wrist 114, varioustransmission lines 220 are required to establish proper communicationbetween, for example, sensors (not shown), actuators 136, 138 and 140(as well as other actuators as will be appreciated by those of skill inthe art) and the control system 150, as well as to provide power (e.g.,electrical, hydraulic or pneumatic power) to such components. Theconfiguration of the robotic wrist assembly 114 allows the transmissionlines 220 to be conveniently harnessed and maintained with many of thetransmission lines 220 being conveyed through and at least partiallyconcealed within the robotic wrist 114.

For example, an annulus 222 may be defined within the opening 174 of theyaw bearing 176, such as by the positioning of an inner sleeve 223within the opening and spaced apart from the inner wall thereof. Theannulus 222 may serve as a transmission line path or raceway. Sometransmission lines 220, such as those associated with the delivery unit115 and placement head 116, may extend from the annulus 222 above therobotic wrist 114 and then be partially wrapped, as a bundle 224 oftransmission lines 220, about the roll bearing 184 or some other surfaceof the robotic wrist 114. Thus, as the robotic wrist 114 articulatesthrough its range of motions, the transmission lines 220 are maintainedin a controlled manner and kept from being whipped or slung aroundwhich, as mentioned above, may cause damage to the transmission lines orpose a some other safety hazard.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the inventionincludes all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A fiber redirect system for use in association with a multi-axisrobotic wrist having at least one section configured to articulate abouta pitch axis, a yaw axis and a roll axis, the system comprising: a firstredirect mechanism configured to alter a path of at least one fiber towengaged therewith, the first redirect mechanism being centered about anintersection of the pitch axis and the yaw axis of the multi-axisrobotic wrist; at least a second redirect mechanism configured to alterthe path of the at least one fiber tow, the at least a second redirectmechanism being centered about an intersection of the yaw axis and theroll axis of the multi-axis robotic wrist.
 2. The fiber redirect systemclaim 1, wherein the at least one redirect mechanism further comprises athird redirect mechanism centered about the roll axis of the multi-axisrobotic wrist.
 3. The fiber redirect system of claim 2, wherein the atleast one fiber tow comprises a first tow band having a first pluralityof spaced apart collimated fiber tows and at least a second tow bandhaving a second plurality of spaced apart collimated fiber tows, thefirst tow band being spaced apart from the at least a second tow band,and wherein the first redirect mechanism, the second redirect mechanismand the third redirect mechanism each includes a first redirect rollerfor engagement with the first tow band and at least a second redirectroller for engagement with the at least a second tow band.
 4. The fiberredirect system of claim 3, wherein the third redirect mechanism isconfigured to redirect a path of the first tow band and a path of the atleast a second tow band so as to cause the first tow band and the atleast a second tow band to converge and collimate with one another. 5.The fiber redirect system of claim 2, wherein the at least one fiber towincludes a plurality of fiber tows and wherein the first, second andthird redirect mechanisms are configured to define a collective fiberpath of the plurality of fiber tows which passes through the pitch, yawand roll axes.
 6. A robotic wrist for a fiber placement systemcomprising: a first section; a second section coupled with the firstsection; a third section coupled with the second section, wherein thefirst section, the second section and the third section are configuredto articulate about a first axis, the second section and the thirdsection are configured to articulate about a second axis and the thirdsection is configured to articulate about third axis; and at least oneredirect mechanism configured to alter a path of at least one fiber towengaged therewith, the at least one redirect mechanism being centeredabout at least one of an intersection of the first axis and the secondaxis and an intersection of the second axis and the third axis.
 7. Therobotic wrist of claim 6, wherein the first axis is a pitch axis of therobotic wrist, the second axis is a yaw axis of the robotic wrist andthe third axis is a roll axis of the robotic wrist, and wherein the atleast one redirect mechanism further includes a first redirect mechanismcentered about the intersection of the pitch axis and the yaw axis and asecond redirect mechanism centered about the intersection of the yawaxis and the roll axis.
 8. The robotic wrist of claim 7, wherein the atleast one redirect mechanism further includes a third redirect mechanismcentered about the roll axis, and wherein the at least one fiber towincludes a first tow band having a first plurality of spaced apartcollimated fiber tows and at least a second tow band having a secondplurality of spaced apart collimated fiber tows, the first tow bandbeing spaced apart from the at least a second tow band.
 9. The roboticwrist of claim 8, wherein the first, second and third redirectmechanisms each includes a first redirect roller for engagement with thefirst tow band and at least a second redirect roller for engagement withthe at least a second tow band.
 10. The robotic wrist of claim 9,wherein the third redirect mechanism is configured to redirect a path ofthe first tow band and a path of the at least a second tow band so as tocause the first tow band and the at least a second tow band to convergeand collimate with one another.
 11. The robotic wrist of claim 8,wherein the at least one fiber tow includes a plurality of fiber towsand wherein the first, second and third redirect mechanisms areconfigured to define a collective fiber path of the plurality of fibertows which passes through the pitch, yaw and roll axes.
 12. The roboticwrist of claim 8, further comprising a first bearing coupled between thefirst section and the second section to accommodate relative rotation ofthe second section and the first section about the second axis, whereinan opening is defined through the first bearing and wherein a path ofthe at least one fiber tow extends through the opening of the firstbearing between the first redirect mechanism and the second redirectmechanism.
 13. The robotic wrist of claim 12, further comprising asecond bearing coupled between the second section and the third sectionto accommodate relative rotation of the third section and the firstsection about the third axis, wherein an opening is defined through thesecond bearing and wherein the path of the at least one fiber towextends through the opening of the second bearing between the secondredirect mechanism and the third redirect mechanism.
 14. The roboticwrist of claim 13, further comprising structure defining an annulusabout the opening of the first bearing, the annulus being configured toreceive at least one transmission line therethrough.
 15. The roboticwrist of claim 6, further comprising a placement head coupled with thethird section and configured to apply a portion of the at least onefiber tow proximate a surface of a mandrel or proximate a surface of awork piece disposed about the mandrel.
 16. The robotic wrist of claim15, further comprising a consolidating member configured to contact theapplied portion of the at least one fiber tow and press the appliedportion against an underlying surface.
 17. The robotic wrist of claim16, further comprising at least one actuator configured to motivate therobotic wrist about at least one of the first, second and third axes.18. The robotic wrist of claim 17, wherein the at least one actuator isconfigured to motivate the first, second and third sections about thefirst axis.
 19. The robotic wrist of claim 17, wherein the at least oneactuator is configured to motivate the second and third section aboutthe second axis.
 20. The robotic wrist of claim 17, wherein the at leastone actuator is configured to motivate the third section about the thirdaxis.
 21. The robotic wrist of claim 17, wherein the at least oneactuator is configured to be operatively coupled with a control system.22. A fiber placement system comprising: a creel assembly including asupply of at least one fiber tow; and a robotic wrist comprising: afirst section; a second section coupled with the first section; and athird section coupled with the second section, wherein the firstsection, the second section and the third section are configured toarticulate about a first axis, the second section and the third sectionare configured to articulate about a second axis and the third sectionis configured to articulate about a third axis; at least one redirectmechanism configured to alter a path of the at least one fiber towengaged therewith, the at least one redirect mechanism being centeredabout at least one of an intersection of the first axis and the secondaxis and an intersection of the second axis and the third axis.
 23. Thefiber placement system of claim 22, wherein the creel assembly furthercomprises at least one tensioning device for maintaining the at leastone fiber tow at a desired level of tension.
 24. The fiber placementsystem of claim 23, further comprising a structural platform, whereinthe robotic wrist is movably positioned on the structural platform. 25.The fiber placement system of claim 24, wherein the first axis is apitch axis of the robotic wrist, the second axis is a yaw axis of therobotic wrist and the third axis is a roll axis of the robotic wrist,and wherein the at least one redirect mechanism further includes a firstredirect mechanism centered about the intersection of the pitch axis andthe yaw axis and a second redirect mechanism centered about theintersection of the yaw axis and the roll axis.
 26. The fiber placementsystem of claim 25, wherein the at least one redirect mechanism furtherincludes a third redirect mechanism centered about the roll axis. 27.The fiber placement system of claim 26, wherein the supply of the atleast one fiber tow further includes a plurality of spools, wherein eachspool of the plurality provides an individual fiber tow.
 28. The fiberplacement system of claim 27, wherein the creel assembly includesstructure for gathering a first plurality of individual fiber tows fromthe plurality of spools to form a first tow band of collimated fibertows and for gathering at least a second plurality of individual fibertows from the plurality of spools to form at least a second tow band ofcollimated fiber tows.
 29. The fiber placement system of claim 28,wherein the first, second and third redirect mechanisms each includes afirst redirect roller for engagement with the first tow band and atleast a second redirect roller for engagement with the at least a secondtow band.
 30. The fiber placement system of claim 29, wherein the thirdredirect mechanism is configured to redirect a path of the first towband and a path of the at least a second tow band so as to cause thefirst tow band and the at least a second tow band to converge andcollimate with one another.
 31. The robotic wrist of claim 26, whereinthe at least one fiber tow includes a plurality of fiber tows andwherein the first, second and third redirect mechanisms are configuredto define a collective fiber path of the plurality of fiber tows whichpasses through the first, second and third axes.
 32. The fiber placementsystem of claim 26, further comprising a mandrel holder positionedadjacent the robotic wrist and configured to rotate a mandrel about adefined axis.
 33. The fiber placement system of claim 32, furthercomprising a placement head coupled with the third section andconfigured to apply a portion of the at least one fiber tow proximate asurface of the mandrel or proximate a surface of a work piece disposedabout the mandrel.
 34. The fiber placement system of claim 33, furthercomprising a consolidating member configured to contact the appliedportion of the at least one fiber tow and press the applied portionagainst an underlying surface.
 35. The fiber placement system of claim34, further comprising at least one actuator configured to motivate therobotic wrist about at least one of the first, second and third axes.36. The fiber placement system of claim 35, wherein the at least oneactuator is configured to motivate the first, second and third sectionsabout the first axis.
 37. The fiber placement system of claim 35,wherein the at least one actuator is configured to motivate the secondand third section about the second axis.
 38. The fiber placement systemof claim 35, wherein the at least one actuator is configured to motivatethe third section about the third axis.
 39. The fiber placement systemof claim 35, further comprising a control system operatively coupledwith the at least one actuator.
 40. The fiber placement system of claim26, further comprising a first bearing coupled between the first sectionand the second section to accommodate relative rotation of the secondsection and first section about the second axis, wherein an opening isdefined through the first bearing and wherein a path of the at least onefiber tow extends through the opening of the first bearing between thefirst redirect mechanism and the second redirect mechanism.
 41. Thefiber placement system of claim 40, further comprising a second bearingcoupled between the second section and the third section to accommodaterelative rotation of the third section and the first section about thethird axis, wherein an opening is defined through the second bearing andwherein the path of the at least one fiber tow extends through theopening of the second bearing between the second redirect mechanism andthe third redirect mechanism.
 42. A method of conveying at least onefiber tow from a creel assembly to a placement head of a fiber placementsystem, the method comprising: coupling a robotic wrist with theplacement head and configuring the robotic wrist to be movable about afirst axis, a second axis and third axis; locating a first redirectmechanism to be centered about an intersection of the first axis and thesecond axis; locating a second redirect mechanism to be centered aboutan intersection of the second axis and the third axis; locating a thirdredirect mechanism to be centered about the third axis; passing the atleast one fiber tow from the creel assembly to the first redirectmechanism; passing the at least one fiber tow from the first redirectmechanism to the second redirect mechanism; and passing the at least onefiber tow from the second redirect mechanism to the third redirectmechanism and from the third redirect mechanism to the placement head.43. The method according claim 42, wherein the at least one fiber towincludes a plurality of fiber tows and wherein the method furthercomprises dividing the plurality of fiber tows into a first tow band ofcollimated fiber tows and at least a second tow band of collimated fibertows.
 44. The method according to claim 43, further comprisingmaintaining the first tow band and the at least a second tow band spacedapart as they are passed from the creel assembly to the third redirectmechanism.
 45. The method according to claim 44, further comprisingjoining the first tow band and the at least a second tow band into asingle tow band containing all of the plurality of fiber tows as thefirst tow band and the at least a second tow band pass from the thirdredirect mechanism to the placement head.
 46. The method according toclaim 42, further comprising defining the first axis as a pitch axis,defining the second axis as a yaw axis, and defining the third axis as aroll axis.
 47. A method of conveying a plurality of fiber tows, themethod comprising: providing a robotic wrist having at least one sectionconfigured to articulate about a first axis, a second axis and a thirdaxis; arranging the plurality of fiber tows into a first collimated towband and at least a second collimated tow band spaced apart from thefirst collimated tow band; defining a collective fiber path to passthrough at least one of an intersection of the first axis and the secondaxis and an intersection of the second axis and the third axis anddefining a portion of the collective fiber path to be along the thirdaxis; and maintaining the first collimated tow band and the at least asecond collimated tow band substantially symmetrically about thecollective fiber path.
 48. The method according claim 47, furthercomprising merging the first tow band and the at least a second tow bandinto a combined collimated tow band at a position along the third axis.49. The method according to claim 47, further comprising defining thefirst axis as a pitch axis, defining the second axis as a yaw axis, anddefining the third axis as a roll axis.